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ON CHROMIC ACID AS A BLEACHING AGENT. 341 
ART. LXXIV.— ON CHROMIC ACID AS A BLEACHING AGENT, 
AND ON A CHEAP AND EASY MEANS OF RECOVERING IT. 
By Charles Watt, Sen. 
Chromic acid has of late years become a very important 
agent in the bleaching of various articles, and particularly 
tallow and oils, more especially palm-oil. The best method 
therefore of using and then recovering it, so that it may 
again be employed, and the expense of the biclu'omate of 
potash, every time the chromic acid is required, be saved^ 
cannot fail to prove of great advantage to ail large con- 
sumers of this article. 
About twelve years since, after numerous experiments 
and much application, I found that no agent was so effectual 
for bleaching foul, dark and offensive tallows and deep- 
coloured oils (namely, palm, linseed and rape oils) as the 
chromic acid. My only consideration therefore was, in wliat 
manner to obtain it in the cheapest form sufficiently pure 
for the intended purposes ; and the deep red salt, the bichro- 
mate of potash, was that from the decomposition of which 
I obtained the acid, in the following manner: — 
To bleach half a ton of dark tallow or high-coloured oils, 
from five to ten pounds of the bichromate of potash is re- 
quired, and from it the chromic acid is liberated by decom- 
posing the salt thus : — 
The bichromate, well-bruised, is put into an earthenware, 
wooden or leaden vessel (not iron, as the acids act on it,) 
and about four times as much hot water is then poured into 
it; the salt is then to be well stirred ; afterwards about one 
and a half pounds of sulphuric acid (for every pound of 
bichromate) is carefully introduced, and the stirring is con- 
tinued until the whole of the salt is dissolved. This liquid 
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